Even if you had a rare (almost vanishingly small probability) high side failure, that "problem is that you have too much power. As if too much power is a bad thing!
Experienced one in a C+, Nick. At night, in an unlit, off helipad area, just before TDP. Following the EF drill (landing back, as we were in the process of doing, having been told to terminate the take off by ATC) causes the Nr to very rapidly go to over speed once the collective is lowered. Not at all pleasant.
Diagnosis is the problem. The failed DECU ran the engine all the way up.